Microsoft planned this week to announce that it was broadening the virtualization rights for Windows Vista, but decided at the last minute to reverse course and stick with existing limits.

The software maker had briefed reporters and analysts on plans to allow the Home versions of Vista to run in virtual machines, addressing criticisms from virtualization enthusiasts and Mac users who had chafed at having to buy one of the two priciest versions of Windows in order to run Vista in a virtual machine.

Software like Parallels Desktop for the Mac or Microsoft's own Virtual PC for Windows allow multiple operating systems to run simultaneously. When it announced licensing rules for Vista last year, Microsoft said that only Vista Business and Vista Ultimate could run as guest operating systems. The company said virtualization presents inherent security risks and that it hoped by limiting which versions of the OS could act as virtual machines, only sophisticated users and businesses would employ the tactic.

On the Mac in particular, though, virtualization has become a consumer feature and many people wanted to use the Home versions of Vista, which Microsoft executives concede present no additional security risk.

The company said in interviews this week that it was still concerned about the security risks, but said it was going to make the change and leave the choice up to users.

"Virtualization enthusiasts would like to make that choice," said Scott Woodgate, a director in the Windows Business Group. "We're really responding to that feedback."

Earlier this week, when Microsoft was believed to be planning to make the licensing changes, Parallels praised the software maker and said it was pleased it had listened to customers.

"When we got the news we were obviously very, very happy," Benjamin Rudolph, Parallels director of corporate communications, said Monday before Microsoft changed its mind. In that interview, Rudolph said that his users had struggled to understand Microsoft's rationale for limiting which versions of Vista could run alongside the Mac OS. "They want to use Vista, but they were a little confused as to why they had to pay $400."

After Microsoft's reversal, Rudolph expressed disappointment with the decision.

"While we're disappointed that Microsoft won't be changing the Vista (license agrement) to permit users to run all versions of Vista in a virtual machine, it is ultimately up to Microsoft to decide how they want to license their own software, and we respect their decision," Rudolph said in an e-mail to CNET News.com. "We'll definitely keep working with Microsoft on this issue."

Microsoft provided little explanation for the about-face.

"Microsoft has reassessed the Windows virtualization policy and decided that we will maintain the original policy announced last fall," the software maker said in a statement late Tuesday